Solid rockets are propulsion devices which operate by thrust generated from the combustion of a rocket propellant. Solid rocket propellants are comprised of fuel, oxidizer, and additives. A typical solid rocket propellant has approximately 70 percent solid oxidizer such as ammonium perchlorate, 15 percent metallic fuel such as aluminum powder, 12 percent binder fuel such as polymeric hydrocarbon material, and 3 percent additives. The range, or distance the rocket can travel, is determined by the maximum weight of propellant (or more specifically by the weight of the fuel) which can be loaded into the rocket. It is important to note that in these rockets, 70 percent of the weight of the propellant is oxidizer. The remaining 30 percent is fuel.
If it were not necessary for the rocket to incorporate oxidizer in the propellant along with the fuel, and if it were possible to acquire oxidizer as the rocket moved through the air, then the entire propellant could be replaced by fuel. This would yield substantial increases in the range or distance the rocket can travel.
A ducted rocket is a propulsion device in which an air duct or scoop is attached to the device to acquire the oxidizer (air) during flight. FIG. 1 shows the schematic of a ducted rocket. There are two combustion chambers. In the primary combustion chamber, a solid fuel undergoes a low order, incomplete combustion reaction which generates fuel gases and particles which escape the primary combustion chamber through a valve and injector shown in the figure. The fuel gases which are the products of incomplete combustion in the primary, include combustible materials such as low molecular weight hydrocarbon species, hydrogen, carbon, carbon monoxide, and other oxidizable species. As the gases and particles enter the secondary combustor, ram air is captured by the inlet, and ducted into the secondary combustor to complete the oxidation process. The hot exhaust gases from the secondary combustor exit through the nozzle, producing thrust for the ducted rocket engine.
Fuel for the solid fuel gas generator has been a problem, and has been the subject of several research efforts. In some cases, oxidizers are mixed at low level with hydrocarbon polymeric materials to provide a solid fuel gas generator. In other approaches, energetic binders have been mixed with combustible solid materials to give a solid fuel gas generator. The most energetic solid fuel gas generators use metal particles as a means of obtaining high energy and high density. Examples are magnesium, aluminum, boron, or zirconium powders incorporated in a binder. While these materials generally perform satisfactorily, they generate smoke in the exhaust from the secondary (due to metallic oxide particles such as aluminum oxide), and are generally unsuited for rocket and missile applications in which it is desired to have a smokeless exhaust plume. In these instances, efforts have been made to incorporate carbon in various forms as a solid additive in the composition of the solid fuel gas generator. Carbon has been known to exist in two pure forms, diamond and graphite, and a number of impure forms, such as coal or soot. Previous experience has shown that solid fuel gas generators in which carbon is included have two main problems. The first problem is that the inclusion of carbon in the solid fuel gas generator introduces particles which must be ejected into the secondary chamber. This is an energy absorbing process which tends to decrease the burning rate of the solid fuel in the gas generator. The second problem is the difficulty in getting carbon to burn once it has entered the secondary combustion chamber. The difficulty in getting complete combustion of the carbon results in extraordinarily long residence times in the secondary combustor in order to get the carbon completely burned.
Therefore, the current status of the art in formulating solid fuel gas generator composition for a ducted rocket (or for other rocket applications) is to attempt to use baffles in the secondary combustion, swirl generation engineering approaches, or simply to build an extraordinarily long combustion chamber.
Therefore, a primary object of this invention is to provide a solution to the problem of complete combustion of carbon in a ducted rocket, or the rocket application, meanwhile retaining the smokelessness inherent in the use of carbon, and the high density available.